- Always allow RAW_PART to be opened, regardless of the partition table.
- Never do partition translation on RAW_PART; it's always offset 0.
- Always make sure the disklabel is read from RAW_PART.
- Make *strategy() return values consistent.
This fixes a condition where a bogus partition table could be written
to the disk from SYS_INST, and the user had no way to rewrite with
a correct partition table, since RAW_PART would be invalid.
thorpej